1. Field of the Invention
This invention relates to storage batteries, and more particularly, to a battery container having flexible ribs for positioning and supporting one or more battery cell elements in one or more cell compartments.
2. Description of the Prior Art
The cell elements of conventional storage batteries are formed of multiple positive and negative grids or plates coated with an electrochemical paste and interleaved with inert separator material to form plate stacks. The number and thickness of positive and negative plates in the plate stack as well as the number of cell elements determine a battery""s energy capacity. Increasing the number of plates in the cell elements increases its energy capacity, while decreasing the number of the plates decreases its energy capacity. At the same time, increasing or decreasing the number and thickness of the plates also varies the overall thickness of the cell elements.
For multi-cell batteries, individual cell elements are disposed in cell compartments of a battery housing and are electrically connected together but remain physically separated. In order to ensure proper electrical connection and battery performance, the cell element must be securely disposed within the cell compartment. Partitions are formed in the battery housing to define the necessary cell compartment size for each cell element without being too big so that the cell element is unsecured or being too small so that the cell element does not fit or is damaged when inserted into the cell compartment. Since the overall battery thickness of the cell element varies according to energy capacity requirements and design parameters, manufacturers often maintain a large inventory of battery housings.
A number of methods have been devised to reduce the number of battery housings needed for various cell element sizes. Some manufacturers use a finite set of battery housings molded to define incrementally different-sized cell compartments and change the thickness of the plates and/or separator material as needed. For example, if a cell element has a small number of plates, then thicker separators are used to fill the cell compartments. However, the separation between the plates in the cell element should be consistent so that the resistivity between the plates is maintained constant. Changing the separator thickness, therefore, adversely affects the electrical performance of the battery.
Alternatively, a rigid spacer can be inserted around a cell element inserted into a larger cell compartment. This method requires that a number of spacers be molded to accommodate the difference in thickness between the various cell elements and cell compartments. U.S. Pat. No. 5,558,958 discloses an improvement upon a rigid spacer by using a flexible spacer, this spacer has a U-shaped sheet with vertical ribs molded of a flexible material such that the cell element can be inserted into the spacer and the spacer and cell element can then be inserted into the cell compartment as a unit. The ribs flex as needed according to the difference between the cell element and cell compartment thicknesses. The flexibility of the spacer allows it to be used with various sizes of cell elements and cell compartments. The flexible spacer also dampens vibrations, which adversely affect the electrical performance and life of the battery cell element.
Other manufacturers have horizontal or vertical ribs molded into the partition and end walls. These ribs are molded from the same polypropylene material forming the battery housing, and consequently, the ribs are stiff. Such ribs must be either molded or machined to precisely the correct dimension for each cell element thickness so that the cell element fits within the cell compartment without being damaged. Or, for such battery housings, the separator thickness must be varied, which degrades the performance of the battery, as mentioned above.
Battery containers have been designed with deformable ribs, as described in U.S. Pat. Nos. 3,607,440 and 4,309,818, the disclosures of which are hereby incorporated by reference as though fully set forth herein. These patents disclose battery housings having integrally molded ribs that deform as needed according to the thickness of the cell element. The deformable ribs compensate for variations in thickness of the cell element so that the number of different sized containers needed is reduced. The ribs are typically molded to the partition walls at an angle other than 90 degrees to reduce the amount of rib deformation as well as facilitate the insertion and removal of the cell elements. However, because the ribs are injection-molded of the same battery-grade polypropylene material as the battery housing, the ribs remain sufficiently rigid such that the battery elements could be damaged when inserted. Moreover, these ribs are not adequately resilient to spring back to their original position after prolonged deformation. Instead, the ribs tend to undergo mechanical creep and take on a permanent set in the deformed position, which further limits their flexibility. Additionally, these ribs do not dampen the vibrations commonly associated with use of a battery in automobiles, trucks, farm equipment or other off-road vehicles.
Battery containers also include rib-like projections or rests extending upward from the bottom of the container for supporting the cell elements. Rather than resting the cell elements on the bottom of the container, these projections are used so that electrolytic fluid can circulate through the cell element from the bottom. Typically, the plate rests are rigid and the plates of the cell elements are electrically connected at the top of the container to battery straps which are welded to opposing straps through the partition walls, as known in the art. Throughout the life of lead-acid batteries, the plates in the cell elements corrode and expand in size. Since the cell element is fixed in place at the top of the container, the plates tend to expand laterally and downwardly. However, the rigid plate rests limit the downward growth and cause the upper comers of the expanding plates to rotate upwardly about the strap connection points at the top of the container. This causes a number of problems that significantly decrease the operational life of the battery, such as electrical shorting, plate-buckling and contortion of the wires.
The present invention overcomes the deficiencies of the prior art and provides a composite battery container with one or more cell compartments having integral, flexible spacer ribs capable of securely retaining cell elements within a range of thicknesses. Furthermore, the battery container has flexible plate-rest ribs that deform to compensate for typical corrosive plate expansion.
Specifically, the present invention provides an improved battery container including a housing having side walls, end walls and a bottom. The walls and bottom define a single-cell compartment or a plurality of cell compartments. Multiple cell compartments are formed by at least one partition disposed within the space parallel with the end walls. The cell compartments are sized to hold a cell element comprising multiple positive and negative plates alternately interleaved with a plurality of separators. A plurality of resilient flexible spacer ribs are integrally formed with the end walls and/or the partitions to project into the cell compartments and center cell elements of various sizes within the cell compartments. The flexible spacer ribs deform elastically when the cell elements are within the cell compartments and return to an essentially non-deformed position when the cell compartments are empty. The flexible spacer ribs are integrally formed with the end walls, and with the partitions in multi-cell batteries, but their material properties differ.
The walls of the battery housing of the present invention can be made of a suitable sturdy material, such as battery grade polypropylene, while the spacer ribs can be made of a highly resilient, flexible material, such as a thermoplastic elastomer. Thus, the spacer ribs can be integral with the rigid housing, yet be highly flexible.
One object and advantage of the present invention is that the integral spacer ribs can center and secure cell elements of various sizes. This permits the use of one or few battery housing sizes for a wide range of energy capacities without the need for separate inserts. Also, the spacer ribs can be formed without excessive precision as to their length.
Another object and advantage of this invention is that the cell elements can be inserted and removed easily without being damaged. This is especially important for battery containers assembled on automated lines.
The spacer ribs can be molded in any orientation, including vertically, horizontally and diagonally, at a range of acute and obtuse angles from the end walls and partitions, including perpendicular. This and the flexibility of the spacer ribs provides the further object and advantage of a battery housing that can be easily molded and removed from the mold.
Still another object and advantage of this invention is to increase the battery""s overall performance in use. The flexible spacer ribs significantly dampen the performance-degrading vibrations realized by the battery cell elements. Also, the spacer ribs permit the use of a single separator thickness. This promotes a consistent electrical resistance within the cell element and improves battery performance. In one embodiment where the spacer ribs are essentially parallel with the battery housing bottom, the ribs include interruptions spaced along their length. These interruptions improve the charging performance of the battery by promoting mixing of the electrolytic fluid, which reduces stratification of the sulfate in the electrolytic fluid.
The battery container can also include flexible plate-rest ribs, with or without the partition/end wall spacer ribs, integral with the bottom of the housing and projecting into the cell compartments to at least partially support the cell element. The plate-rest ribs are flexible so as to deform when the cell elements extend toward the bottom of the container due to corrosive expansion of one or more of the plates. This provides the additional object and advantage of a battery container that increases the operational life of the battery cell elements by compensating for the corrosive expansion of the plates and mitigating the related adverse effects. Further, although integral to the housing, the plurality of plate-rest ribs are preferably of a different material. This allows the housing to be constructed of sturdy, rigid battery-grade polypropylene and the ribs to be a resilient, flexible thermoplastic elastomer.
The foregoing and other objects and advantages of the invention will appear from the following description. In this description reference is made to accompanying drawings which form a part hereof and in which there is provided by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention.